Potential dead horse: how bad is FF's deep DoF disadvantage?

Can you think of a case where a cell phone is superior to a M4rds camera for photography purposes?

I have shot 4/3 and Olympus C-series cameras for years, and I prefer the smaller sensors for macro, by a lot. They perform better.

If you are going for very deep DOFs (relatively) in a shutter speed limited environment, this is true.

I think that the issue here is that noise does not increase linearly, at least on the digital cameras that I've used. So when you bump up ISO to match the shutter speed and DOF of smaller-sensor cameras, you don't necessarily get an equivalent result.

If the sensors are equally efficient, then the noise will be the same. Modern compacts using sensors with BSI tech will tend to be more efficient than modern DSLR and mirrorless cameras.

You might get a worse result. In fact, I prefer my C8080 to my Olympus 50mm f2.0 for macro, although to be fair, I could probably get a better result from the 50mm macro if I took the time to set up the shots. But I don't want to. That counts against the larger format, because it's a useability issue.

We have to distinguish between which system delivers better results and which system is more convenient to use.

IMHO, FF has too shallow DOF. Photographers struggled for years in all formats to get everything in focus, using elaborate techniques like tilting lenses in large format, and all of a sudden in the digital age being able to get everything in focus easily is a disadvantage! My 50mm 2.0 macro is TOO SHALLOW wide open. It needs to be stopped down considerably, maybe two stops at least, three is better, for head and shoulders shots. And people need SHALLOWER DOF than that? Er, OK.

This photo:

was taken at 100mm f/2 on FF, which is equivalent to 50mm f/1 on 4/3. Granted, it's not a head and shoulders shot. But here are two that are:

Now these were shot at 150mm f/2.8 (75mm f/1.4 on 4/3) and 50mm f/1.4 (25mm f/0.7 on 4/3), and may well represent what you consider a DOF that is "too shallow". Typically, one would aim for deeper DOFs for such a tight framing, such as this:

which was at 150mm f/5.6 (75mm f/2.8 on 4/3). However, even that might be "too shallow" for your tastes, and 150mm f/11 might have been more the ticket.

The point is that FF gives you a wider range of options. If these options do not appeal to you, however, then, for sure, you would be better suited with a smaller format unless some other aspect of FF, such as greater resolution, was important.

FF to me wins on noise and dynamic range.

The noise advantage comes from using a more shallow DOF in low light. The DR advantage comes from using a longer shutter speed for a given DOF at base ISO.

The DOF issue is a loss for FF, and maybe for small-sensor cameras too. APS-C and especially m43 have it about right--you can easily manipulate apertures and distances to get the effects you want. Being in focus is not a bad thing, despite what some people would have you believe.

Particular systems are inherently better than others for particular tasks, and some people find one system to represent a better balance of those factors that matter most to them. For me, even in the case of macro, I find that shallow DOF is often appealing:

70mm f/2.8 on FF (35mm f/1.4 on 4/3) -- although I will certainly stop down as I see fit, for example the photo below was at 70mm f/11 on FF (35mm f/5.6 on 4/3):

In any event, the "appropriate" DOF is a matter of the scene and the aesthetics of the photographer and viewer.